31 BIOLOGY AND ITS MAKERS 



time, of the germinal substance, is a conception of very great 

 extent, and now underlies all discussion of heredity. 



In order to comprehend it, we must first distinguish 

 between the germ-cells and the body-cells. Weismann 

 regards the body, composed of its many cells, as a derivative 

 that becomes simply a vehicle for the germ-cells. Owen's 

 distinction between germ-cells and body-cells, made in 1849, 

 was not of much importance, but in the theory of Weismann 

 it is of vital significance. The germ-cells are the particular 

 ones which carry forward from generation to generation the 

 life of the individual. The body-cells are not inherited di- 

 rectly, but in the transmission of life the germ-cells pass to 

 the succeeding generation, and they in turn have been inher- 

 ited from the previous generation, and, therefore, we have 

 the phenomenon of an unbroken connection with all previous 

 generations. 



When the full significance of this conception comes to us, 

 we see why the germ-cells have an inherited organization of 

 remarkable complexity. This germinal substance embodies 

 all the past history of the living, impressionable protoplasm, 

 which has had an unbroken series of generations. During 

 all time it has been subjected to the molding influence of 

 external circumstances to which it has responded, so that 

 the summation of its experiences becomes in some way 

 embedded within its material substance. Thus we have 

 the germinal elements possessing an inherited organization 

 made up of all the previous experiences of the protoplasm, 

 some of which naturally are much more dominant than the 

 others. 



We have seen that this idea was not first expressed by 

 Weismann; it was a modification of the views of Nussbaum 

 and Hertwig. While it was not his individually, his con- 

 clusions were apparently reached independently. This idea 

 was in the intellectual atmosphere of the times. Several 



